GT125R Performance issues
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Hi,
I’ve purchased a GT125R for my daughter (her choice) but it doesn’t seem to be performing as I would expect, I got the battery tested and it needed replaced which I’ve done, also replaced the spark plugs.
I’ve tested the voltage of the battery when the bike is running and it’s showing 13.3 volt, increasing the rpm and it only goes up to 13.4. ive checked the regulator with the diode check on the multimeter and each pin is the same.
Checking each phase of the stator and its only showing 12.7v AC on each phase and when the rpm’s increased the voltage drops to 8.9v AC on each phase.
Does anyone know what voltage should be on each phase? I couldn’t find anything online. Also would the low voltage affect the performance, it struggles to go above 50mph
Have never worked on a bike until this one but can follow directions and use a multimeter
Thanks for any help on this
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A correction for my stator testing, the original results was with the cables connected to the regulator, with the cable disconnected I get over 80v AC. So not sure if stator is correct voltages or not, the regulator output at 5000rpm fluctuates between 3v and 13.5 DC, if I release the throttle it jumps up to 14.6v for about 1 second.
Would this point to a faulty regulator or stator?
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That would be the regulator
Can you confirm also that each “yellow” wire of the stator unit , outputs identical voltages ? with the reg disconnected while at 5000 rpm ?
Ie.
3 yellow wires
- Yellow A & B = volt?
- Yellow B & C = volt?
- Yellow A & C = volt?
Also a warm welcome to both of you , she made a good choice with the hyosung! – We will get it going no worries about that, there isn’t too much riding happening until Spring time, so Daddy might aswell give it a full once over 😉 . Ignore whatever the last owners did to it, act as if you just bought it blindly and will trace everything under the chassis to make sure its all in spec , then your young lady won’t have to worry too much & just ride.
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Thanks Marcel
the tachometer doesn’t work, but I got someone to rev the bike and keep it stable I’m not sure if above 5000rpm
- Yellow A & B = 82volt
- Yellow B & C = 82volt
- Yellow A & C = 72volt
This is to become her daily driver, she’s moving up from a moped that she’s been on for the past year
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It looks like one of the phases of the stator is on its way out. So I would most definitely look to upgrade the stator unit and regulator (being a married pair ofcourse lest old part ruins the new part)
Is the engine grey or black (OEM colour, not re-sprayed by past keepers) – if in doubt you can always upload the picture of the current stator thats in the bike , due to the fact there is 2 versions that exist
Also some owners actually buy newer flywheels and stators from a 2016 GT125RC to retrofit back inside a 2005-2010 engine.
Hence even on this site , i sell 2 variants of 125cc stators for the GT125 bikes.
I would definitely recommend NGK caps as the OEM caps are just rubbish. (Avoid the “plastic” ngk caps too as they rattle too much) , you want the rubber versions like we do and fresh plugs.
Coils = Keep the oem coils if the primary & secondary resistance are in spec ? (Measure the resistance of the coils without the HT cap attached. Poorly coils do make it hard sometimes to get up to speed if they are wanning (assuming she has had moments of misfire while riding ? or flat-ness in some rev ranges)
Tachometer = Post a picture , 3 variations exist and are tied to the harness the bike uses (as ofcourse there is 3 variations of harnesses Hyosung uses on the Gt125R)
Sorry for digressing , I hope i made some sense. In a nutshelf 85v + at 5k revs is good for a stator at all 3 yellow lines.
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Thanks Marcel,
Here’s a picture of the tachometer, the engine is black but not sure if it’s just painted black, won’t be able to take picture of the stator until tomorrow.
What should the resistance be of the coils?
What’s the benefit of the newer flywheel?
Sorry for all the questions, I’m new to this, never worked on a motorbike, I work in IT
Thanks
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Based on that Tacho, you should have a harness that says “GT250R” with a white tag , near the battery. As all 2005-2009 GT125R (specifically “R” fairing models) use GT250R harnesses from a carby GT250R (they last longer as they are thicker honestly)
If unsure, just got near the battery , along the harness , photograph the tag that’s written on it and i will confirm.
Coils (without HT cap attached)
- Ground to HT wire = max 6.2K ohms (6200)
- Ground to Coil “terminal” connector = 0.01 to 0.10 ohms ( zero point one single ohm)
Nothing good about the RC Flywheels
- Smaller + 18 pole stator = Also discontinued product , costs more than the older black 12/11-pole versions that are far more durable or the upgrade ones. Older flywheels are better. Allows to use OEM stator (pre-2009 black ones) or upgrade versions (but avoid china though!)
((A “LOT” of common charging issues with hyos can sometimes be attributed to knock of stators and regulators. Sometimes they blow batteries or the harness literally catches fire…. Oh yes, we saw all that on Facebook years ago, thats either a GT125, GT250 or even a 650 which has bigger stators!) - OEM stators are OK “dependent” on how the regulator behaves and the bike isnt trying to “piss it” off. The 125cc stators don’t like heated grips (Use KIES Portable Apparel for that winter sizzle! and recommended)
Questios are fine , fire away. You want her happy with it and you pretty much her mechanic!
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LED Lights won’t murder the stator as that’s not even 10 watts drawn out of the stator as the bike runs.
Good job you have a black stator , we can work with that! – Sadly new ones are not made anymore , so we gotta pimp that. with a regulator.
I bet the regulator is either chinese on it or a teeny silver one (which Hyosung recalled/updated to the bigger OEM ones but still not great as it was an “outsourced” part)
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Yes, that’s the teeny one that was so infamous for blowing up. Based on your recent report, these below suit your bike 100% (our regulators will be 3x larger than yours and it is intentional).
As you live in N.I , postage should be free but please send me an email with your postcode , just incase there is no surcharges for certain postcodes but I doubt it!Stator Unit (+ mandatory gasket card/template) (can’t re-use the old one) & various Stainless Bolts (required as OEM bolts are not great!):
Upgrade Magneto Alternator Stator Coil :: GT GV 125 250 + RT RX 125
Regulator Unit
Upgrade Regulator Rectifier [Reg Rec] :: GV GT 125 250 R GTR Hyosung
Oil Filter!
Oil Filter Service Kit & O-Rings – Hyosung GV125 GT125R GT125 GV250 GT250
You should have some good fresh oil ready and inspect your drain plug is all good, you will find oil related tutorial here:
As you want no old shavings or any particles to cling to the new stators. Clean that flywheel drum very well!
https://hyoriders.club/forums/topic/change-oil-filter-hyosung-twins/
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The only extra electrical components someone has added to the bike are led lights but all my tests where done with those disconnected- You must be logged in to reply to this topic.